1. Field of the Invention
The present invention relates to an optical lens system for taking image, and more particularly to an optical lens system for taking image used in a miniaturized digital camera.
2. Description of the Prior Art
In recent years, with the popularity of the mobile phone camera, the optical lens system for taking image has become thinner and thinner, and the electronic imaging sensor of a general digital camera is typically a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) sensor. Due to advances in semiconductor manufacturing, the pixel size of sensors has been reduced continuously, and miniaturized optical lens systems for taking image have increasingly higher resolution. Therefore, there's increasing demand for image quality.
A conventional mobile phone camera usually consists of three lens elements: from the object side to the image side: a first lens element with positive refractive power, a second lens element with negative refractive power and a third lens element with positive refractive power, such as the optical lens system for taking image described in U.S. Pat. No. 7,145,736.
As the pixel size of electronic imaging sensors gradually becomes smaller and smaller, the system requires higher image quality. The conventional optical lens system comprising three lens elements cannot satisfy the requirements of higher resolution optical lens systems.
U.S. Pat. No. 7,365,920 discloses a four-piece lens assembly, in which the first lens element and the second lens element, which are both spherical lens elements, are bonded to each other to form a doublet lens for eliminating chromatic aberration. However, it suffers from the following disadvantages: the freedom of the optical system is insufficient since there are too many spherical lens elements; and the manufacturing difficulty is increased due to the difficult process of bonding glass lens elements.
The present invention mitigates and/or obviates the afore-mentioned disadvantages.